The present invention pertains to a circuit for controlling an electric motor having run and start windings and for connecting the motor to a source of electrical supply. In particular, the invention pertains to a control circuit adapted for use with an electric sump pump motor and for connecting the motor to the control switches therefor and to a source of electrical supply.
Generally, prior art sump pump control circuits for connecting an electric sump pump motor to a source of electrical supply comprise a float operated actuator switch mounted on the motor housing, a centrifugal or other start switch for controlling the start winding mounted on a terminal board located inside the motor housing and conductors for interconnecting the switches and the motor windings to a source of electrical supply. The actuator switch and the terminal board both have electric terminals located thereon for interconnection with the remainder of the circuit. A line cord is generally connected to one pair of terminals on the actuator switch. Another pair of terminals on the actuator switch is connected by two conductors to a first pair of terminals mounted on the terminal board on which the centrifugal switch is mounted. A second pair of terminals on the centrifugal switch terminal board is connected by means of electrical conductors to the motor windings.
The terminals employed for the above-described connections are generally of the push-on or quick-connect type wherein an electrically conducting sleeve secured to the electrical conductor fits over a flat rectangular terminal mounted on a rigid insulating base. The sleeve is assembled to the terminal by pushing it on to the terminal and is retained thereon by friction fit.
One disadvantage of the known electric circuits for controlling electric motors is the multiplicity of terminals and connections needed to interconnect the various parts. The use of a multiplicity of terminals and connections is expensive because of the cost of the parts and the labor needed to assemble the parts. In addition, since in the prior art motor control circuits all the terminals are of one size, it is possible that in the assembly of the circuit the numerous terminals are connected incorrectly so that the motor circuit either does not function properly or is subject to failure. Furthermore, in the sump pump environment it is possible that quick-connect terminal connections will work loose due to vibration caused by operation of the motor and that the circuit will fail. It is, of course, self-evident that the possibility of such failure due to vibration is directly proportional to the number of terminals used in the assembly of the circuit.
In motor control circuits of the type described, it is customary to connect a motor protector switch in series circuit connection with the motor windings. This protector switch is responsive to excessive winding temperatures or current and will open in response thereto thereby deenergizing the motor. Since one of the electrical supply leads is normally grounded it is desirable to connect the protector switch to the ungrounded supply lead, so that, upon opening of the protector switch, the motor windings are completely disconnected from the ungrounded source of electric potential.
In the prior art circuits described, improper connection of the ungrounded supply lead was possible because of the use of identically sized terminals for both supply line lead connections to the motor circuit and subsequent possible errors in assembly. It is desirable to ensure that the grounded supply lead is connected to the side of the motor circuit which is not opened in case of opening of the protector switch. It was also possible in prior art arrangements to short out the motor and power supply by connecting both leads to one of the switch poles.
It is desirable, in motor control circuits, to connect the actuator switch directly to the motor windings, and to have the connecting leads bypass the terminal board upon which the centrifugal switch is mounted. With such an arrangement the junction terminals on the terminal board can be eliminated, the windings can be connected directly to the actuator switch with quick-connect terminations and assembly costs can be avoided.
It is also desirable to use keyed terminals in motor control circuits of the type described so that errors in assembly can be avoided.
It is also desirable in circuits of this type and particularly in the sump pump environment, to connect the line cord lead which is not grounded to the side of the motor circuit which is opened in case of a circuit failure.